Emerald Ash Borer Part III - The Science Makes Progress

November-December 2010

A PATIENT LYING ON A HOSPITAL GURNEY after a car accident is unaware of the number of people working for them. From the kitchen staff to the pharmacist to the hospital administrator, there are many people doing their job to make the patient’s stay as short as possible. The same is true when an invasive insect causes a crisis. The specialists discussed here are only a small part of the team working on both sides of the border to save the North American ash and keep our cities green.

Considered by many to be the miracle tree for cities after Dutch elm disease (DED), the ash was crossed, hybridized and sold across the continent and even farther afield to Beijing, China. Here at home, entire subdivisions were planted with these beautiful and often identical hybrids. The North American ash in China grew and then suddenly died. “Tongue in cheek,” one researcher joking said, “They cut down the North American ash, made them into shipping crates, and sent them back full of six dollar toasters.” Seriously, we don’t know exactly what happened to the ash in Beijing, but we do know our world now has a global economy. We also have years of history dealing with invasives in forestry – and we have scientific tools and experience.

Breakthrough Discovery
A couple years ago, Kathleen Knight of the USDA Northern Research Station in Delaware, Ohio was walking across a bridge with some students when she stopped, suddenly amazed. After days and weeks of inventorying dead ash, standing there before them was a healthy, thriving one. They ran to the tree and immediately examined, photographed and inventoried it.

Knight was so excited she started sending out the photos to colleagues. Their response was quick and varied. One said, “It’s good to keep your enthusiasm but we need to watch and see when it will die.” Jennifer Koch, also of the USDA in Delaware, took the opposite view. “Even if the tree does eventually die of emerald ash borer (EAB), there may be something present we can breed for that allows ash to survive longer than their counterparts. Through breeding, it may be possible to get trees that tolerate EAB even better than these original lingering survivors. Let’s get scion material and graft the trees so that they can be tested. If the original trees identified in the field go on to die, we will have preserved exact copies of them through grafting.” This moment in time gave ash trees the edge in research.

Mixing healthy skepticism with hope, they went to work. Knight’s research scope expanded. New surveys were done and with renewed energy they searched for more healthy ash in EAB ravaged areas. At one site, among 8,000 dead they found about 100 that were “pretty” healthy. These sites are still being monitored with purple traps and EAB continues to be active in the area. Nothing visually can be seen to explain why these trees are either dying more slowly or in some cases thriving. They are usually within twenty to thirty feet of an ash dead of EAB.

“People are excited about my work,” says Knight. “When you’ve seen the devastation, it’s tough to believe there is hope. But it would not be the first time we’ve seen a native tree that is resistant or tolerant to exotic pests. Beech, elm and hemlock trees have been found that are able to survive beech bark disease, Dutch elm disease, and hemlock wooly adelgid, respectively. This is something that does happen in nature.”

Many of these lingering ash are not “resistant” and may not survive long term. However, the excitement at the discovery of these trees has a second component, time. Trees that “linger” are a seed source in the forest allowing the ash to continue until research catches up. Intolerant of shade, ash seedlings and saplings may be shaded out as other species fill in the forest holes. In more rural wild areas, EAB-killed trees are not sprouting from the root as they are in cities. There is a huge potential to lose the genetic diversity of the other native insects that depend directly on ash. On both sides of the border, researchers are attempting to monitor and measure the changes in our forests as the ash dies back, but the task is monumental. Here in Canada, there is also an effort to try and collect seed from diverse areas and species.
One researcher commented, “I hate the term lingering. It implies these trees are in the process state of dying. Some of these trees are not failing, they are beautiful.”Call these trees survivors or lingering or anything you want, but so far they are all green and white ash. High concentration areas of surviving black ash have not been found. This is a huge concern. Koch said, “People don’t know they should be looking. It is only natural that we will find the rare survivor.”

Don List, Ontario sales rep for Bailey Nurseries (www.baileynurseries.com), said, “An EAB resistant tree will be worth millions.”

As I write this, the samples collected from the US surviving ash are grafts on native ash growing in laboratory conditions awaiting testing. Some have bloomed and produced seed.

Hybridization & Resistant Genes
In the 1960s in Manitoba, Dr. Wilbert Ronald was working at the Morden Research Center and crossed Manchurian ash with black ash to develop a cold hardy hybrid resistant to the ash flower bud gall mite. Ronald has retired but some of his trees, now called “Northern Treasure” and “Northern Gold,” were sold to the entomological team at Michigan State. Dr. Eric Rebek, currently of Oklahoma State University, studied the ash hybrids and said, “Emerald ash borer originated on the Asian continent along with Asian species of ash. Following eons of a co-evolutionary chess match between beetle and tree, Manchurian ash and other Asian species have evolved resistance to the beetle. Only when they are under environmental stress do the trees succumb to the beetle. The hybrid cross between a North American (black ash) and Asian species resulted in a tree with no resistance. The resistance gene from the Asian parent was not conferred to the offspring.”

This is not bad news. It is part of the research process. From this work, we know our ash can be crossed successfully with part Chinese ash genetics. It also puts us years ahead of previous hybrid research. These trees are now to be back crossed in search of the resistant gene.

Koch said, “If EAB resistance is a recessive trait, it is very possible that even though first generation hybrids such as Northern Treasure are susceptible, they still may be carriers of resistant genes and if mated with another carrier (susceptible phenotype, has resistance gene) or a resistant tree (such as the backcross back to Manchurian), that a proportion of the progeny resulting from such a cross could be EAB resistant – much like how two brown-eyed parents can sometimes have a blue-eyed child.” 

Knowing hybridization works and knowing we need many types of ash to replace our urban stock, a private group hired some researchers to go to China on the hunt for resistant species. Kris Bachtell and Tony Aiello returned with six Chinese species including five seed types. These are Chinese ash, Manchurian ash, Pax’s ash, Chinese flowering ash and island ash. The material collected was grafted to North American ash and some have flowered producing pollen for more crosses. Because of experience developing a resistant beech and chestnut, new resistant ash are not decades away. However, researchers ask for patience. They want to be positive their trees are resistant before they are released. Although Canadians did play a role in ash genetics, I could find no Canadian currently involved in this work and no indication our governments are funding these programs. Koch said, “We have been working through Rick Durand, the Canadian Nursery and Landscape Association (CNLA) Research Coordinator, as a liaison, with Dr. Ronald Wilbert. He has sent us tissue samples to confirm via DNA analysis that our Northern Treasure accession is the same as the originally released cultivar. This work is in progress. We have also discussed other areas of potential collaboration and would welcome any sort of collaborative efforts with Canadian researchers.” 

One Canadian angle in the search for EAB resistance is the blue ash. Dr. Barry Lyons of the Canadian Forest Service says they have confirmed by bio-assay that EAB will not feed readily on blue ash. He also confirms some blue ash continue healthy at “ground zero in Windsor.”

Here’s my question to you: Is anyone crossing blue ash with Chinese ash?

A Closer Look at China
Once again due to efforts in the US, our forests received a boost because of the foresight of Dr. Juli Gould with the USDA Animal Plant Health Inspection Service and Dr. Leah Bauer, USDA Forest Service, and their motivated teams. They are working on two completely separate programs and their work began when someone wondered what would happen if the planned eradication of EAB failed.

Here’s the background research: Dr. Jim Smith of Michigan State collected EAB from Asia and North America and did genetic studies. “It was difficult to get Asian specimens,” he said. “EAB is not abundant in Asia.” He only got one from Japan and found it very different. This limited sampling makes it impossible to be emphatic about the results but it was a huge step forward. The N. American EAB were genetically similar to each other and to EAB tested from the Port Key Bay and from the Beijing areas of China. This means there is a ‘bottleneck’ in the genetic diversity of EAB in North America so it is likely they were introduced just once or at least only from this one area of China.”

Based on this, Bauer and Gould went to China to discover why the EAB is only a periodic pest in these specific regions. They found four specific potential biological control agents. One was discounted immediately as it might sting humans. The remaining three went through a huge process of examination and public consultation (most US states have organized science panels that carefully weigh the risks/benefits of releasing versus not releasing biocontrol agents). To date, all EAB-infested states agree that the potential benefits outweigh any potential risks. Pennsylvania, Wisconsin and New York have approved permits for release of these parasitoids but are gathering background information to identify optimal release sites. More information on this is available at: http://www.regulations.gov/fdmspublic/component/main?main=DocketDetail&d=APHIS-2007-0060.

Fighting Nature With Nature
The biological control agents are as follows. Spathius agrili is a larval ectoparasitoid. It lays its eggs on EAB larvae and eventually consumes the larvae. Tetrastichus planipennisi is a larval endoparasitoid. It lays its eggs in EAB larvae. Both are now being reared in a brand new laboratory designed and built for this purpose. Thousands of each were released in 2010 in Minnesota, Illinois, Indiana, West Virginia, Maryland, Kentucky, Ohio and Michigan. There is the possibility they will be released in Pennsylvania, Wisconsin and New York in 2011. Oobius agrili is an egg parasitoid. It lays its eggs in the EAB egg. This third parasitoid has not been released in large numbers yet as the rearing program is not ready.

Gould describes her parasitoids as “wimpy.” They don’t sting because they can’t. They have no venom. They have no stinger, only an ovipositor. None of the insects in this family sting. They are beneficial insects and look like ants with wings. In laboratory testing, it was found there was some limited attack on the bronze birch borer and two-lined chestnut borer, but only when EAB was not available and this was not unexpected. “They don’t like to be reared on anything but ash. Spathium prefer to oviposit in the presence of ash volities. And they don’t overwinter as adults so they won’t swarm into houses like the Asian multi-coloured lady beetle.”

As with all biocontrol programs, there is much to be learned. Constant monitoring and studying continue as this program moves forward. We do know all three species are surviving US winters. They are consuming EAB in the wild. “No other species of such borers has been targeting for biocontrol so potential for success (in controlling EAB) can not be predicted.”

Dr. Sandy Smith of the University of Toronto said, “When biocontrol goes well no one notices, but when it goes wrong there is a public uproar. Compare the purple loosestrife program to the Asian lady bug. Obtaining a parasitoid from an invasive’s home country is called ‘classical’ biological control. This is what the US is doing. All biocontrol programs need extensive time, research, money and questions. If we don’t ask the questions, we won’t get the answers.”

What’s Happening in Canada?
On the homefront, are our researchers involved in the US parasitoid project both as collaborators and in fact checking to determine how these wimps will affect both Ontario urban and wilderness forests? As we all know, these beneficial insects will not check their passports at the border.

Taylor Scarr (MNR) said, “In Canada, the research typically would focus on areas not being addressed in the US or we would collaborate with US researchers.”

One of Sandy Smith’s students, Lucas Roscoe, is working on a different type of a biocontrol program. He is following a native wasp (also wimpy) called Phasgono-phora sulcata. There was almost no information about the biology of this helpful native insect other then it is feeding on EAB at a 40% rate in one area of Ontario. It was found feeding on EAB in the US, but not at this rate. The idea is to study this insect and learn its habits and needs so it could potentially be reared in a lab and released in EAB hot spots to slow the spread. This idea is still in the concept stage of research.

Roscoe has worked the last two summers in Sault Ste. Marie (Canada) with Dr. Barry Lyons studying Phasgono-phora sulcata and they’ve learned a lot to help the process. This insect is native and is found everywhere there is bronze birch borer (BBB). In fact, if you see a birch dying of BBB in the spring, look closely and you will likely see this larval endoparasitoid. It is the most common parasitoid in Canada of metallic wood boring beetles and it has successfully made the host shift to EAB.

In the lab, they give the adults a little honey but otherwise they don’t feed. The wasp larvae consume Buprestidae beetles (metallic wood boring beetles) in the larval stage. Lyons says, “It’s hard to know the wasp is there. It is right inside the host.” It will eventually kill the host and chew its way out of the tree. They are gregarious so they will lay a single egg on a single host. Lyons continues, “They can build up high populations in the wild on EAB.”

Another Canadian researcher, Dr. George Kyei-Poku and his team from Natural Resources Canada, Great Lakes Forestry Centre, are working on a different biocontrol angle to help control EAB. They started collecting samples of EAB in southern Ontario (Windsor, Sarnia and London) and examined them for diseases lethal to EAB. They found four that are native to Canada.

The species under study include Beauveria, Lecanicillium, Metarhizium (entomopathogenic fungi) and Paecilomyces (a nematode or roundworm belonging to the subgenus Oscheius). Kyei-Poku still has a couple areas to investigate. First, we need to know which (or will all) the conditions kill EAB while allowing the insect to live long enough to share infection? Second, can the spores exist in sunlight so they can be placed in a trap? And finally, what is the best way to spread the fungi? There is some hope that testing for this promising project could start in 2011.

Also working on EAB projects and also funded by Ontario Ministry of Natural Resources with Guelph University is Dr. Steve Marshall and his graduate student Phil Careless. They are working with the Cerceris wasp as a method of detecting EAB. Editor’s note: In the March/April 2009 issue of the Ontario Arborist (Bits & Chips, pp. 6-7), the CFIA Cercersis Project was looking for monitoring volunteers. Visit www.cerceris.info for updates. Secondly, Dr. Gard Otis from the University of Guelph, a Canadian TREE Fund grant recipient, reported on his blue ash research in the November 2006 issue.

Every biocontrol researcher I spoke with reinforced how aware they are of the risks and benefits of their work. Whether a classical biocontrol or native biocontrol agent is released is a political decision based on “need versus risk.” Researchers attempt to check, double check and question again and again. They all want time and support to double check their work. They want the public to understand that “rush work” is not acceptable in their field.

Here in Ontario Scarr says, “We are partnered with CFS (Canadian Forest Service) and the lead agency CFIA (Canadian Food Inspection Agency). CFIA is using corrugated green plastic prism-shaped traps hung in ash trees. The traps are baited with leaf volatiles and are coated with a sticky film to catch insects. These are at over 500 locations.”

Dr. Peter Silk is an Insect Chemical Ecologist working out of Fredericton, New Brunswick with NRCan and he is more than excited about the speed of their discoveries. Silk said so far it appears EAB is attracted by three things, vision, host volatiles and sex pheromones. For vision, the traps are brightly coloured either purple or green. Green traps are hung five metres up and tend to be male-dominant in trap capture while purple traps catch a mix of males and females depending on trap height and the attractants used. The host volatiles are Phoebe oil, Manuka oil or leaf alcohol, Z3-hexenol. They are using female produced sex pheromones 3Z-lactone. Silk says, “This is NOT the end of the story. More is coming out about the mating behaviour everyday that involves new discoveries that will likely affect trap capture, mating, oviposition behaviour and more.”

Scarr said another area of research OMNR provided funding for was work by Dr. Blair Helson into potential insecticides that could be injected into ash trees to protect them from EAB. This led to the 2006 application for an emergency registration of Confidor (active ingredient: imidacloprid, manufactured by Bayer). Bayer did not pursue a full registration and it expired after one year. In 2007, they applied for emergency registration of TreeAzin (active ingredient: azadirachtin, distributed by BioForest Technologies) in London.

Scarr: “This product has been used the last few years by tree care companies and shows good efficacy. The distributor has applied to the Pest Management Regulatory Agency of Health Canada for a full registration.” (Emergency registrations must be requested by a user, not by a manufacturer or distributor. Hence OMNR applied for the emergency registration on behalf of the partners involved so that the product would be available for use in Ontario.)

Here’s a few more research tidbits. Dr. Chris McQuarrie of the Canadian Forest Service is investigating the main causes of EAB mortality and trying to determine the times in the insect’s life cycle when it is most vulnerable. Dr. David Kreutzweiser is coordinating another program examining the impacts of EAB in southwestern Ontario. His team is monitoring tree succession and changes to biodiversity in response to EAB.

One point noted by biocontrol researchers in the US could help those searching for genetic resistance. To date, no one has confirmed anything visible to distinguish with 100% accuracy the difference between the resistant ash and the non-resistant. However, peeling the bark of a resistant tree required significantly more energy then peeling the bark of a non-resistant tree. All the researchers meet at EAB conferences to discuss and share this type of information. They know sharing and cooperating is the road to successful EAB management.

Silk said, “This is not a competition to see who can get the ‘best’ trap, we truly want to unravel the chemical ecology of this bug. The key now in my view is to have a trap that has sufficient sensitivity to detect low level populations with no/few false negatives. So keep listening and you will see new things surfacing on this.”

Dr. S. Smith contributed, “We need the public to stop thinking of the urban forest like horticulturalists (or as specimen trees). Foresters see the connections. Every forest is different. We need to see the forest as a system, not a collection of individual trees, especially our urban forests.”

Last Words
In hindsight, it is easy to point out mistakes – like the idea we could eradicate or contain EAB for any length of time – in the way EAB research was managed in the beginning. It must be noted that just 10 years ago this insect was almost completely unknown. There wasn’t even much documentation on the entire Buprestidae family. Here in North America, our politicians and researchers made educated guesses. Some were costly mistakes. Maybe they should be called educational tools instead.

Today, graduate students at the University of Toronto are working on biological control of invasive forest insects in addition to EAB. These include Sirex woodwasp, Tomicus pine shoot beetle, and invasive plants such as dog-strangling vine as well as invasive earthworms. Dr. March, professor emeritus in chemistry at Trent University and an internationally-renowned expert in his field, has bark volatiles from oak and maple. We’ve made a lot of progress in ten years. The lessons we learned weren’t wasted energy and money, they will help us face future concerns that haven’t even surfaced yet. It’s just part of routine urban forest maintenance, right? 

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